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Heat loads and cryogenics

Heat loads and cryogenics. L.Tavian, D. Delikaris CERN, Cryogenics Group, Technology Department Accelerators & Technology Sector. Content. Introduction Heat loads H eat inleaks Resistive heating Beam induced heat load Cooling capacity requirement Conclusions. Cryogenics at CERN.

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Heat loads and cryogenics

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  1. Heat loads and cryogenics L.Tavian, D. Delikaris CERN, Cryogenics Group, Technology Department Accelerators & Technology Sector HE-LHC'10 Workshop

  2. Content • Introduction • Heat loads • Heat inleaks • Resistive heating • Beam induced heat load • Cooling capacity requirement • Conclusions HE-LHC'10 Workshop

  3. Cryogenics at CERN HE-LHC HE-LHC'10 Workshop

  4. Introduction • Scaling from LHC loads • Three main temperature levels • Thermal shield (TS): 50 and 75 K • Heat intercept (HI): 4.6 K & Beam screen (BS): 4.6-20 K (40-60 K or 85-100 K as an alternative compatible with vacuum specification) • Cold mass(CM): 2 K • 8 cryogenic sectors • One cryogenic plant per continuous cryostat (arc + dispersion suppressors) • Dedicated cryogenic plants for high-load insertions (RF, IT…) as for HL-LHC • Continuous cryostat (arc + dispersion suppressors) only considered in the following HE-LHC'10 Workshop

  5. Heat inleaks (w/o contingency) • Assumption: thermal performance of the HE-LHC cryostat (magnet + cryogenic distribution QRL) similar to the one of the LHC cryomagnet. • Contingency (on heat inleaks); Reminder: LHC contingency factor = 1.5 • Overcapacity (on cryogenic plant’s refrigeration power) HE-LHC'10 Workshop

  6. Resistive heating in SC splices • Resistive heating proportional to: • the square of the magnet current, • the splice electrical resistance • the number of splices HE-LHC'10 Workshop

  7. Current lead cooling • Assumptions: • HE-LHC is using the same type of HTS current lead as the LHC with the same cooling performance, i.e. 54 mg/s per kA of helium between 20 and 300 K • as the optics of the HE-LHC are not yet fully defined the number of individually powered magnets is not known  total current entering or exiting proportional to the main magnet current • as for the LHC, it is assumed that high-load sectors enter two times more current than low-load sectors HE-LHC'10 Workshop

  8. Beam-induced load: Scaling laws HE-LHC'10 Workshop

  9. Beam-induced loads(for BS operating between 4.6 and 20 K) • The biggest change concerns the synchrotron-radiation load, which increases by a factor 17 ! HE-LHC'10 Workshop

  10. Operating the beam screen at higher temperature • Operating beam screen at higher temperature will reduce the specific entropic cost of refrigeration, but: • As the electrical resistivity of the copper on the beam-screen surface increases with the temperature, the image-current load will also increase proportionally • The temperature difference between the beam screen and the cold bore will increase, i.e. the heat inleaks on the cold mass will increase as well • Changing the operating conditions and the specific heat load has a direct impact on the cooling capillary diameter • Two alternative temperature ranges compatible with vacuum requirement: • 40-60 K • 85-100 K HE-LHC'10 Workshop

  11. Copper electrical resistivity • Image current: 0.44 W/m for 4.6-20 K temperature range 2.4 W/m for 40-60 K temperature range 9.8 W/m for 85-100 K temperature range X 22 X 5.5 HE-LHC'10 Workshop

  12. CM heat load vs. BS temperature (See LHC Project Note 330) • Cold bore heat load: 0.006 W/m for 4.6-20 K temperature range 0.17 W/m for 40-60 K temperature range0.71 W/m for 85-100 K temperature range X 120 X 30 HE-LHC'10 Workshop

  13. Beam screen cooling capillary • 40-60 K temperature range  minimum diameter ! HE-LHC'10 Workshop

  14. Summary of specific cryogenic heat loads HE-LHC'10 Workshop

  15. Cold mass cooling • LHC cooling scheme limited to 0.9 W/m (sub-cooling heat exchanger), i.e. not compatible with the 85-100 K BS temperature range. • Cooling at 2 K: reduced conduction in superfluid helium to extract the heat from the coil. LHC HE-LHC Apparent thermal conductivity of superfluid helium HE-LHC'10 Workshop

  16. Continuous cryostat cooling capacity per sector (values in brackets: equivalent entropic capacity in kW at 4.5 K) • Assumptions:- Continuous cryostat length: 2800 m- Overcapacity factor: 1.5 (for each temperature level) as for LHC plants *: 2.4 kW at 1.8 K plus 0.3 kW at 4.5 K HE-LHC'10 Workshop

  17. Equivalent entropic capacity HE-LHC'10 Workshop

  18. Electrical input power for continuous-cryostat refrigerators Assuming a performance coefficient factor of 250 W/W (electrical / @4.5 K) HE-LHC'10 Workshop

  19. Concluding remarks[1/2] • No contingency has been introduced in the numbers • A lot of assumptions have to be confirmed ( e.g. the splice resistance and number, the main magnet current, the current-leads distribution and number, and the cryostat performance) • The optimization of the refrigeration cycle has still to be done (wrt temperature levels) • Transient heat loads (ramp/de-ramp, fast de-ramp, quench), have still to be considered in order to define the correct level of buffering • The insertion loads have still to be considered (dedicated new cryoplants as for HL-LHC) HE-LHC'10 Workshop

  20. Concluding remarks[2/2] • Depending on the cooling scenario, up to 9 temperature levels have to be distributed along the continuous cryostats to supply or recover the different cooling loops  A rationalization study has to be done for reducing the number of distribution headers like: • operating the beam screen and the thermal shield with the same temperature range (40-60 K) • cooling the resistive part of HTS current lead with a helium flow at a higher temperature and pressure (e.g. 40 K, 20 bar) • At the end of the LHC (2030), the LHC (& former LEP) cryogenics will reach 30 to 40 years operation; Initially specified for a 20-year operation, major overhauling has to be considered for the equipments re-affected to the HE-LHC project (cryoplants, QRL, distribution boxes…) HE-LHC'10 Workshop

  21. Additional slide Rationalization options • Temperature range (9 levels) • Inlet: 50 K (TS), 40 K (BS), 20 K (CL), 4.6 K • Outlet: 300 K (CL), 75 K (TS), 60 K (BS), 4 K (Very Low Pumping) • Quench recovery T • Rationalization options: • TS & BS @ 40-60 K • CL LHC 20-300 K (but regulated @ 50 K, saving distribution headers) • CL HE-LHC @ 40-300 K, 20b (taking profit from the TS & BS option) • Leading to reduced Temperature range (6 levels) • Inlet: 40 K, 20 b (TS, BS, CL), 4.6 K • Outlet: 300 K (CL), 60 K (TS, BS), 4 K (Very Low Pumping) • Quench recovery T HE-LHC'10 Workshop

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